In September 2004 NOAA initiated a program to monitor the flow of the DWBC in near-real-time. This new program uses moored inverted echo sounders, some of which are additionally equipped with bottom pressure gauges and deep current meters. Data from these instruments is acoustically downloaded by a passing research vessel about every six months without actually recovering the instruments.
Location of the inverted echo sounders.
The data is then brought back to the lab where it is processed. A preliminary comparison completed using data obtained during 1995-1997 has shown that this combination of instruments can reproduce the transport of a more traditional picket-fence of current meter moorings to within the accuracy of the current meter array (Meinen et al., 2004).
For those unfamiliar with inverted echo sounders, here are a few basic facts about these systems:
- Small package about 0.6 meters tall that is moored about 1 meter off the bottom
- Sends out a 10 kHz (or 12 kHz) sound pulse and measures the amount of time that a signal takes to go up to the sea surface, reflect, and return.
- Provides hourly data, which is generally low-pass filtered and subsampled to daily
- Combined with hydrography from the region, the IES provides profiles of temperature, salinity, and specific volume anomaly.
- Some IESs are additionally equipped with pressure gauges (we call these PIES) and sometimes with an acoustic current meter head (we call these C-PIES).
- Modern IESs can transmit their data acoustically to passing ships without being recovered.
One of the inverted echo sounders moored east of Abaco Island (Bahamas) before its deployment aboard the NOAA Ship Ronald H. Brown.